Showing papers by "Dong-Soo Kim published in 2020"

LEAP-UCD-2017 Comparison of Centrifuge Test Results

Abstract: This paper compares experimental results from every facility for LEAP-UCD-2017. The specified experiment consisted of a submerged medium-dense clean sand with a 5-degree slope subjected to 1 Hz ramped sine wave base motion in a rigid container. The ground motions and soil density were intentionally varied from experiment to experiment in hopes of defining the slope of the relational trend between response (e.g., displacement, pore pressure), intensity of shaking, and density or relative density. This paper is also intended to serve as a useful starting point for overview of the experimental results and to help others find specific experiments if they want to select a subset for further analysis. The results of the experiments show significant differences between each other, but the responses show a significant correlation, R2 ~ 0.7–0.8, to the known variation of the input parameters.

LEAP-UCD-2017 V. 1.01 Model Specifications

Abstract: This paper describes the specifications developed by and distributed to all of the centrifuge test facilities involved in LEAP-UCD-2017. The specified experiment consisted of a submerged medium dense clean sand with a 5-degree slope subjected to 1 Hz ramped sine wave base motion in a rigid container. This document describes the detailed geometry, sensor locations, methods of preparation, quality control, shaking motions, surface markers, and surface survey techniques.

LEAP-2017: Comparison of the Type-B Numerical Simulations with Centrifuge Test Results

Abstract: This paper presents comparisons of 11 sets of Type-B numerical simulations with the results of a selected set of centrifuge tests conducted in the LEAP-2017 project. Time histories of accelerations, excess pore water pressures, and lateral displacement of the ground surface are compared to the results of nine centrifuge tests. A number of numerical simulations showed trends similar to those observed in the experiments. While achieving a close match to all measured responses (accelerations, pore pressures, and displacements) is quite challenging, the numerical simulations show promising capabilities that can be further improved with the availability of additional high-quality experimental results.

Centrifuge modelling of drained pullout and compression cyclic behaviour of suction bucket

Abstract: In recent years, the tripod suction bucket foundation has been considered as an option to support offshore wind turbines. In an offshore environment, a wind turbine foundation should be designed co...

Soil plug heave induced by suction bucket installation on sand via centrifuge model tests

Abstract: Suction pressure created during suction bucket installation may disturb the surrounding soil and affect its properties. Soil heaving can also occur owing to upward seepage inside the bucket embedde...

Centrifuge modeling of disconnected piled raft using vertical pushover tests

Abstract: A disconnected piled raft (DPR) foundation has been introduced as an effective pile design to reduce the vertical loading experienced by the pile. The characterization of DPRs has focused on the load transfer mechanism, foundation and soil settlement, bearing capacity, load distribution, and bending moment of the piles. DPR piles can act to increase the bearing capacity of the ground, and DPRs can reduce settlement while securing the bearing capacity. In this study, centrifuge model tests are performed to simulate the static behavior of DPRs under actual stress conditions. The behaviors of the DPR foundation for axial load, axial load distribution among the piles, and bending moment are compared to those of the connected piled raft foundation to understand the complex behaviors of DPRs. The centrifuge test results show that DPRs help reduce the pile axial load and bending moment during vertical loading. In addition, DPRs show smaller vertical settlement than shallow foundations. Therefore, we confirm that DPRs can be applied in foundation design as settlement reducers.

LEAP-UCD-2017 Centrifuge Test at KAIST

Abstract: Since the earthquakes of Niigata (Japan, 1964) and Alaska (USA, 1964), the dangers of liquefaction have been highlighted and research into liquefaction has been actively performed. Particularly, as part of the provision and verification of liquefaction data through physical modeling by using centrifuge and numerical prediction, the Liquefaction Experiments Analysis Project (LEAP) was launched. The purpose of the recent LEAP-UCD-2017, in which nine facilities participated, was to evaluate the uncertainty and repeatability of response in a previous study for LEAP-GWU-2015. The ground models were prepared in a rigid box with a 5° sloping model with relative densities of 85 and 50% by using Ottawa sand. The models were subjected to nondestructive and destructive motions based on a ground motion consisting of a tapered 1 Hz sine wave. This paper describes not only the experimental procedure in detail but also the difference in the sensor response of the ground model corresponding to the relative density of 85 and 50% during liquefaction. Moreover, it provides data for permanent horizontal–vertical displacement through liquefaction and for validation of the numerical model.

LeAP-Asia-2019: Validation of centrifuge experiments and generalized scaling law onliquefaction-induced lateral spreading

Abstract: 1 Dept. of Civil, Environmental and Applied Systems Eng., Kansai University, 3-3-35, Yamate-cho, Suita, Osaka 564-8680, Japan. 2 Faculty of Societal Safety Science, Kansai University, 7-1, Hakubai-cho, Takatsuki, Osaka 569-1098, Japan. Dept. of Civil and Environmental Engineering, Ehime University, 3 Bunkyo-cho, Matsuyama, 790-8577, Japan. 4 Dept. of Civil and Environmental Eng., Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo, 152-8552, Japan. Disaster Prevention Research Institute, Kyoto University, Gokasho Uji 611-0011, Japan. Dept. of Engineering, Cambridge University, UK Dept. of Civil and Environmental Engineering, George Washington University, Washington DC, USA Dept. of Geotechnique Eau et Risques, IFSTTAR, Bouguenais, France Dept. of Civil and Environmental Engineering, Korean Advanced Institute of Science and Technology, KAIST, Republic of Korea Dept. of Civil Engineering, National Central University, Jhongli City, Taoyuan, Taiwan Dept. of Civil and Environmental Engineering, Rensselaer Polytechnic Institute, Troy, New York, USA Dept. of Civil and Environmental Engineering, University of California, Davis, USA Dept. of Civil Engineering, Institute of Geotechnical Engineering, Zhejiang University, Hangzhou 310058, P. R. China

Closed Form Solutions for Predicting Lateral Response of Tripod Suction Pile for Offshore Wind Turbine Foundation

Abstract: This study presents a simplified analysis technique capable of predicting the dynamic behavior of a tripod suction pile subjected to a horizontal load. The first natural frequency of the system, horizontal displacement, and allowable rotation angle at the pile head were set as target physical quantities in accordance with substructure design requirements. In consideration of the physical characteristics of the tripod suction pile, the analysis was extended to the single pile-multi-pile-tripod-tower part to derive the influence factors. A possible displacement response function that could be applied to the intermediate pile range was also proposed. Thereafter, a detailed design was determined using an integrated load analysis, which included a turbine based on the basic design of simplified analysis method. Furthermore, the dynamic behavior of the offshore wind turbine at each installation stage was predicted using a numerical analysis and measured via field tests. The displacement at the pile head and the predicted value of the first natural frequency of the system were compared using the field-measured and numerical analysis values. The first natural frequency value produced by the simple analysis method showed an error range within 1%, and the displacement at the pile head also satisfied the structural design requirements. Therefore, this method provides a quick and accurate solution to the lateral response of tripod suction piles as foundations for offshore wind turbines.

Optimization of Two Soil–Structure Interaction Parameters Using Dynamic Centrifuge Tests and an Analytical Approach

Abstract: The response of the structure subjected to an earthquake load is greatly affected by the properties of the structure and soil so it is very important to accurately determine the characteristics of the structure and soil for analysis. However, studies on the effective profile depth where soil properties are determined, have been conducted in the presence of restricted conditions (i.e., surface foundation, linear soil properties), and without any considerations on damping. In case of the effective height of structure that affects its rocking behavior, it was only theoretically or empirically determined. In addition, most previously published studies on soil–structure interaction (SSI) focused on limited effects and parameters (e.g., rocking behavior, embedment effect, effective profile depth, spring constant, and damping coefficient) and not on comprehensive SSI parameters. Furthermore, no detailed validation procedure has been set in place which made it difficult to validate the SSI parameters. Since the effective height of structure and effective profile depth are the basis of all the input parameters of SSI analysis, it is important to validate and determine them. Therefore, in this study, the procedure used to optimize the two SSI parameters was established based on an analytical approach that considered all the possible SSI parameters that were investigated from conventional codes and studies and physical model tests. As a result of this study, the optimum values of the effective height of the structure and effective profile depth were respectively determined according to (a) the height from the bottom part of the foundation to the center of the mass of the superstructure, and according to (b) the depth at values equal to four times the radius of the foundation.

Centrifuge benchmark testing of laterally loaded monopiles in sand

Abstract: The large diameter monopile is a commonly used foundation concept for offshore wind turbines. The advantages of geometrical simplicity and reliable performance make it often the most attractive solution. Despite the concept’s high popularity, optimisation of the current design models can still be made. To address fundamental understanding of modelling effects in centrifuge testing of laterally loaded monopiles in sand, a large coordinated centrifuge-testing program across 11 different centrifuge centres worldwide is ongoing. This extended abstract presents the initial results of global benchmark testing.

Centrifuge Modeling of Embankment Failure due to Underground Cavity and Its Electrical Resistivity Monitoring

Abstract: In this paper, embankment or levee failure due to the interaction between a cavity within an embankment body and high water level was simulated in a centrifuge test and monitored by electrical resistivity tomography (ERT) survey technique. As the centrifuge modeling is an effective research tool for levee stability analysis and the ERT survey is generally adopted in field for health monitoring of levee, physical modeling of levee stability problem and its monitoring by the ERT survey in the centrifuge provides a great opportunity for researchers. Initially, 1 g preliminary test was performed for simulating the underground cavity using a buried ice block to ensure the simulation of such cavity in the centrifuge model. Subsequently, 20 g centrifuge test was performed. At the 20 g-level, over the three stages’ water level in river side was maintained to simulate expansion of the underground cavity with increase in groundwater level. Continuous ERT survey was simultaneously conducted to monitor the variation of internal state of the embankment body. During the final high water level, subsidence of levee surface occurred at the vertical location on top of the cavity which can lead to embankment failure. The ERT results (two dimensional contour plots) from the centrifuge test correspond well to the expected process of levee subsidence caused by upward development of inner cavity by showing definite resistivity difference between the cavity and adjacent soil. From the centrifuge test, it is concluded that the cavity within the embankment body could induce failure upon interacting with the high water level, and the ERT monitoring could effectively capture the geotechnical process which shows the upward development of underground cavity.

Difference and Sensitivity Analyses of the LEAP-2017 Experiments

Abstract: The experimental results of LEAP (Liquefaction Experiments and Analysis Projects) centrifuge test replicas of a saturated sloping deposit are used to assess the sensitivity of soil accelerations to variability in input motion and soil deposition. A difference metric is used to quantify the dissimilarities between recorded acceleration time histories. This metric is uniquely decomposed in terms of four difference component measures associated with phase, frequency shift, amplitude at 1 Hz, and amplitude of frequency components higher than 2 Hz (2 + Hz). The sensitivity of the deposit response accelerations to differences in input motion amplitude at 1 Hz and 2 + Hz and cone penetration resistance (used as a measure reflecting soil deposition and initial grain packing condition) was obtained using a Gaussian process-based kriging. These accelerations were found to be more sensitive to variations in cone penetration resistance values than to the amplitude of the input motion 1 Hz and 2 + Hz (frequency) components. The sensitivity functions associated with this resistance parameter were found to be substantially nonlinear.